The science post of the weekend with Mathilde Fontez, editor-in-chief ofEpsiloon, take us on the island of Barro Colorado, in Panama, where researchers have observed monkeys consuming a lot of ripe fruit.
franceinfo: Have these researchers discovered that monkeys tend to consume alcohol by picking up overripe fruit?
Mathilde Fontez: Yes, this is confirmation of an old hypothesis: the “drunk monkey” hypothesis. Our attraction to alcohol, to us humans, would come from afar: from our primate ancestors, who would have started eating fermented fruits, rotten fruits, and which therefore contain some percents of ethanol. It is this hypothesis which has just been confirmed by observations made for the first time on monkeys in their natural environment, in the Panamanian forest.
The American researchers who carried out the study picked up the fruits that remained on the ground, in the territory of the “spider monkeys”, to deduce their diet. And they found an alcohol consumption. They then confirmed the discovery, by urinalysis.
So monkeys prefer rotten fruit?
The study shows that they like alcohol, but also sugar. They like cocktails. They leave fruits that are really highly fermented, which contain several percent ethanol. And they choose the ones that are only 1 or 2% ethanol, which are still sweet.
The researchers also showed that these monkeys have an excellent olfactory sensitivity to ethanol: they know how to recognize the smell of alcohol, and choose their fruits based on that. And no doubt that their metabolism has evolved to support the consumption of alcohol.
So they evolved to drink?
That’s quite right. It was genetic studies that showed the phenomenon, in 2015, this time in chimpanzees and gorillas, which are our closest cousins. It all started 10 million years ago. At that time, climate change would have gradually turned some forests into grasslands; arboreal monkeys would have come down from the trees, and they would have discovered, on the ground, the fallen fruits: damaged fruits that they would have started to consume, as a food supplement.
That’s how they would have, by natural selection, developed an ability to break down this poison – alcohol. To limit the psychotropic effects, while drawing energy from it: remember that 1g of ethanol contains almost twice as many calories as 1g of carbohydrates. This is why today chimpanzees, gorillas, and humans are able to metabolize alcohol 40 times better than other species.
Basically, if we are able to enjoy an aperitif, without falling from our chair, it is because monkeys, a long time ago, started eating rotten fruit.